Donald Trump famously doesn’t trust computers. At an event on New Year’s Eve, he told reporters, “You know, if you have something really important, write it out and have it delivered by courier, the old-fashioned way.” Well, a pen and paper screwed him when his bodyguard recently displayed the cellphone number of the Secretary of Defense for all the world to see.

What you see in the picture above is Keith Schiller, Trump’s longtime bodyguard, walking with the president and carrying a folder with Defense Secretary Jim Mattis’s private cellphone number written on a sticky note. We are running the photo blurred but it’s still widely available on the AP wire service. Just to give you an idea of how clear the number is, here’s a zoomed-in version:

Photo: AP

Yeah, it’s almost like they did it on purpose. But no, they’re probably just dumb.

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The Washington Post ran this photo on a story about Schiller on May 11th. A concerned reader contacted the Post about the number being visible. And after confirming that it is indeed General Mattis’s phone number, the Post swapped the image out on its website. Gizmodo called the number and it still went to Jim “Mad Dog” Mattis’s voicemail at the time of this post’s publication. It also appears that Mattis is using an iPhone. You get the blue bubble when texting him.

Screenshot: Gizmodo

So, while Trump is embroiled in controversy over leaking classified intelligence to the Russian government, his bodyguard leaked the phone number of the Secretary of Defense, and Trump is still ranting on Twitter about how the FBI can’t find leakers.

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RIP Mattis’s inbox, but there’s more to be concerned about. Security experts have warned for years that just having a person’s cellphone number can give hackers a ton of opportunities to break into a person’s phone. A number of techniques have been used to hack cellphones and surely there are methods that aren’t widely known—the kind of methods that say, other governments might be aware of.

In 2013, an encryption flaw in SIM cards was found that put around 750 million phones at risk. There’s also a famous vulnerability in the global system of mobile phone networks that is known as Signalling System No 7 (SS7). It was discovered in 2014, and if someone has the expertise to exploit it, they could gain full access to the targeted phone’s communications. The vulnerability continues to exist and will only be fixed if telecoms step up and do something about it.